Wind-induced dust generation and transport mechanics on a bare agricultural field☆
Introduction
The Clean Air Act, amended in 1990, required the US Environmental Protection Agency (USEPA) to establish National Ambient Air Quality Standards (NAAQS). These standards set limits on airborne pollutants, including particulate matter, considered harmful to the public and the environment. The standards were designed to protect public health and welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings [1]. Particulate matter is subdivided by size. Particles with a mass median aerodynamic diameter of less than 10 μm are called PM10 and particles with a mass median aerodynamic diameter of less than 2.5 μm are called PM2.5. PM10 particles pose health risks because they can be inhaled into the respiratory system and the PM2.5 pose a greater risk because they can be inhaled deeply into the lungs. Although many pollutants originate from industrial and other anthropogenic sources, geologic materials may contribute significant airborne particulate matter.
Much is known and has been written about wind as a geological process causing aeolian sediment transport and deposition of particulate matter [2], [3], [4], [5], [6]. Interest continues in this topic as shown by recent conferences in Africa and West Asia [7], Europe [8] and the United States [9]. Airborne particles originating from geologic materials can have many sources and may pose threats to humans and animals, depending upon the size and geochemistry of the particles and any materials adsorbed onto the particles. In this paper, we limit our discussion to the emission and transport of suspended particles (or fugitive dust) from earth surfaces due to the force of the wind, a process often called wind erosion. Although sources of suspended dust are numerous and varied, similar processes occur when dust is emitted from deserts, dry lake beds, agricultural fields, dirt roads, construction sites, and other areas where the surface is bare and erodible particles are exposed to the force of winds.
Particles moved by the wind can range up to about 1 mm in diameter, but particles travelling great distances are usually much smaller (<100 μm). Particles of fine dust (<20 μm) have a low settling velocity, even under low wind speeds, and may be transported great distances and kept suspended in the atmosphere for a very long time [10]. Wind erosion is a significant source of fine dust and PM10, particularly in regions of highly erodible soils [11], [12], [13].
Field studies of airborne dust produced at or near the origin of intense dust sources are difficult to conduct yet numerous studies have been reported [14], [15], [16], [17], [18], [19], [20], [21], [22]. Most studies have focused on total suspended dust <20 μm. However, due to the interest in PM10 in the NAAQS, recent studies in the US have focused on PM10 emissions [20], [21], [22], [23], [24].
Fine dust is generally emitted due to the force of saltating particles impacting the soil surface [6], [14], [25]. Recent work in silty loessial soils of the US Pacific Northwest suggests that fine dust may also be entrained into the atmosphere due to the direct force of the wind, without saltation bombardment [24]. Work by Gillette et al. [20] has related horizontal mass flux of sediment to the vertical flux of PM10 particles for a large sandy playa lake in California. The lake represents an unusual large eroding surface. Information on the vertical flux of PM10 particles is needed to determine the potential particulate hazard of eroding surfaces. Since the USEPA designated the southern half of the Owens Valley as a ‘Serious’ PM10 non-attainment area, a State Implementation Plan was developed that calls for the control of dust on 43 km2 of the lake bed [23].
However, most eroding surfaces are often much smaller than the Owens Lake bed and the study of suspended dust poses significant challenges. If the field is very small, the total amount of emitted dust may be determined by simply measuring the vertical profile of dust concentrations of the plume and multiplying by the wind speed to obtain a horizontal flux. However, this may not be practical if the field is so large that the entire plume cannot be sampled or estimated or if there are many heterogeneous source areas in large fields.
Many studies use the gradient method, described by Gillette [26], to estimate vertical flux of suspended dust. The application of the gradient method in agricultural fields is not clear. The method requires measurement of dust at two heights and seems to assume a fully developed dust plume, yet no studies have described the effect of dust sensors height or placement in relation to a developing dust plume close to the dust source on vertical dust flux measurements. In addition, agricultural fields are often so variable or small that horizontal emissions are not uniform. In this paper, we test the hypothesis that large variations in vertical dust flux may arise depending upon sensor and tower placement in a small agricultural field. In addition, we describe the effect of horizontal mass flux on vertical dust flux in small fields and demonstrate the importance of wind direction and sampler placement.
Section snippets
Experimental site
The study site was located in the southern Great Plains of west Texas at the United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Wind Erosion and Water Conservation Research Unit field station in Big Spring, Texas (32.2702N, 101.4865W). The climate is semiarid with a mean annual temperature of 17.1 °C, mean annual precipitation of 470 mm and mean annual wind speed of 8 m s−1. The study was conducted on an Amarillo fine sandy loam (13% clay, 78% sand and 0.3% organic
Results and discussion
A summary of the wind profile characteristics determined for periods when saltation was active and dust concentration measurements were collected is listed in Table 1. Dust concentration measurements were collected in the late morning and early afternoon on each day.
The observation periods ranged from 240 to 395 min long. The wind originated from the west–southwest (252–258° mean wind direction) on all days. The mean 2 m wind speeds were lower than the mean threshold wind speeds during the same
Conclusions
Estimates of vertical dust flux are often obtained by measuring dust concentrations at two heights and then applying a diffusion equation similar to Eq. (3). No standard heights at which to make dust concentration measurements are often specified. In cases where the suspended dust is thoroughly mixed with a uniform concentration near the surface in the atmospheric boundary layer, specification of measurement heights may not be needed. This was the case for the west tower on March 4. Eroding
Acknowledgements
The authors are grateful for the diligent efforts provided by Ace Berry, Charles Yates and James Davis for site installation, data collection and processing assistance. The authors also thank the anonymous reviewers for their valuable assistance in improving this manuscript.
References (44)
- et al.
Dust concentrations and particle-size characteristic of an intense dust haze event: inland delta region, Mali, West Africa
Atmos. Environ.
(1996) - et al.
Wind erosion in a semiarid agricultural area of Spain: the WELSONS project
Catena
(2003) - et al.
Soil crusting on sandy soils and its influence on wind erosion
Catena
(2003) - et al.
The blown sand flux over a sandy surface: a wind tunnel investigation on the fetch effect
Geomorphology
(2004) - USEPA, United States Environmental Protection Agency, National Ambient Air Quality Standards web page,...
- et al.
Wind as a Geological Process on Earth, Mars, Venus and Titan
(1985) Aeolian Dusts and Deposits
(1987)- et al.
Desert Geomorphology
(1993) Physics and Modelling of Wind Erosion
(2000)
Wind erosion in Europe
Catena Spec. Issue
PM10 source apportionment study in Bullhead City, Arizona
J. Air Waste Manage. Assoc.
Tropospheric aerosols form major dust storms of the southwestern United States
J. Appl. Meteorol.
Measurement of fugitive PM10 emissions from selected agricultural practices in the San Joaquin Valley
Characteristics of airborne particles produced by wind erosion of sandy soil, High Plains of west Texas
Soil Sci.
Grain-size characteristics of sediment transported during dust storms
J. Sediment. Petrol.
Soil losses by wind erosion
Soil Sci. Soc. Am. J.
Sediment fluxes and particle grain-size characteristics of wind-eroded sediments in southeastern Australia
Earth Surf. Proc. Landforms
The Wolfforth field experiment: a wind erosion study
Soil Sci.
Cited by (97)
Numerical simulation of the airflow at the world's largest concentrated solar power plant in a desert region
2022, Solar EnergyCitation Excerpt :Additionally, blowing sand particles will accumulate in and around protective walls and fences (Fig. 1d), or even climb over them and into the plant, causing serious demage. Due to the generally flat topography and sparse vegetation cover in desert regions, near-surface aeolian sand activity is frequent at plants (Pelt and Zobeck, 2006). Because of the structural differences between CSP plants, they experience varying effects and risks from wind and blowing sand.
Windbreak efficiency in controlling wind erosion and particulate matter concentrations from farmlands
2021, Agriculture, Ecosystems and EnvironmentCitation Excerpt :Windblown dust transported along the wind direction resulted in higher PMs concentrations on the leeward side of the windbreak (Table 3). Previous findings by Zobeck and Van Pelt (2006) investigating PM10 concentrations along a transect of bare agricultural land indicated that a higher PM10 flux (2.5–3 times greater) was recorded at a sampling site 100 m downwind of a previous sampling site. These findings indicate that it is difficult to distinguish PMs concentrations emitted from a sampling point from those transported from upwind regions.
An improved approach to estimate sand-driving winds
2021, Journal of Cleaner Production
- ☆
Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.